def update_time_span(self):
    """更新时间跨度显示"""
    start_dt = self.start_time.dateTime().toPyDateTime()
    end_dt = self.end_time.dateTime().toPyDateTime()
    time_diff = end_dt - start_dt
    days = time_diff.days
    hours = time_diff.seconds // 3600
    minutes = (time_diff.seconds % 3600) // 60
    
    span_text = "时间跨度: "
    if days > 0:
        span_text += f"{days}天 "
    if hours > 0:
        span_text += f"{hours}小时 "
    if minutes > 0:
        span_text += f"{minutes}分钟"
        
    self.time_span_label.setText(span_text) 